The present invention relates to a process for measuring the velocity of flow of a fluid by determining the transit time of an electrochemically generated marker over a reference distance, and to a flowmeter using the process.
In the past, a large number of different types of flowmeters have been proposed which measure the time of transit of a tracer or tag over a predetermined distance. One form of tracer is a visible dye or float that can be manually observed and timed. This form of tracer is obviously not suitable for making continuous velocity measurements and cannot be used at great depths. Another form of tracer employs radioactive material. Although a tracer of this type can be sensed by an instrument, it possesses certain hazards. When employing either form of tracer, it is very difficult, if not impossible, to store an adequate supply of dye or radioactive material at the location of the instrument to permit unattended operation for an extended period of time. It is also necessary to physically eject the tracer into the fluid. It is very difficult and expensive to design and build an ejection mechanism that will operate effectively particularly for extended periods of time when subjected to severe marine fouling.
More recently it has been proposed to produce a thermal tracer by heating a volume of fluid above the ambient temperature of the surrounding fluid. This technique is described in a number of publications, including U.S. Pat. Nos. 3,399,566 and 4,335,616. A temperature sensor such as a thermometer or thermistor senses the passage of the heated fluid whereby the transit time of the heated fluid over a predetermined distance can be measured. Unfortunately, this technique is limited to gases and is totally unsuitable for liquids. Gases typically have low thermal inertia and are poor conductors of heat. Thus they are relatively easy to tag and the tag persists in gases over a time longer than the transit time. Liquids have relatively large thermal inertia and good thermal conductivity. Thus in liquids, temperature tags become poorly defined prior to the time it takes the tag to reach the sensor and the accuracy, effectiveness, response time, etc. of such a device has been very poor.
The present invention relates to a process for measuring the flow velocity of a liquid which employs electrochemically generated marking elements and which gives a precision comparable to that of the usual measurements which make use of the mechanics of fluids, whilst remaining simple and inexpensive.
The invention also relates to such a process of measurement, where the marking element is produced from the fluid itself.